The following relates to the semiconductor arts. It especially relates to Si/SiGe interband tunneling diode (ITD) structures such as Esaki-like Si/SiGe ITD's, Si/SiGe resonant interband tunneling diodes (i.e., RITD's), and the like, and will be described with particular reference thereto. However, the following will also find application in conjunction with Esaki-like interband tunneling diode device structures in other material systems, and in electronic and optoelectronic devices incorporating same.
Tunnel diodes have numerous potential and actual applications, including but not limited to local oscillators, frequency locking circuits, advanced SRAM circuits, highly integrated analog/digital converters, high speed digital latches, and so forth. Tunneling is a very fast phenomenon; hence ITD-based devices typically are operable at high frequencies.
Interband tunneling diode structures include degenerately doped n-type and p-type regions, sometimes very thin, in sufficiently close relative proximity so that electrons and holes can cross the p/n junction by quantum mechanical tunneling. In some ITD structures, the degenerate doping required is achieved using delta doping to concentrate the doping density to approximately the solid solubility limit. If the delta doping is very thin and of high enough doping density, it can also lead to quantum well regions that confine carriers. With a quantum well on the p-side and n-side of the p/n junction diode, resonant interband tunneling (e.g. RITD) can occur when the quantum wells are spaced closed enough for an overlap of the carrier wavefunctions. The ITD structure is challenging to produce, because dopant segregation and dopant diffusion during growth lowers the doping density and degrades the negative differential resistance (NDR). Using low temperature epitaxy reduces dopant movement during growth which increases the tunneling that manifests in an elevated peak current and a larger peak-to-valley current ratio (PVCR).
However, low temperature epitaxy also typically introduces higher point defect concentrations which increase the valley current of the negative differential resistance region. Point defect concentrations can be reduced by post-growth annealing; however, the annealing can induce solid state dopant diffusion that degrades the peak current of the negative differential resistance region. In some silicon-based ITD structures, a silicon-germanium layer is interposed between the degenerately p-doped and degenerately n-doped regions to reduce diffusion of dopants across the p/n junction during the post-growth anneal. The interposed silicon-germanium layer provides improved thermal stability of the doping profile during post-growth annealing; however, the thermal budget is still found to be limited by dopant diffusion.
The present invention contemplates improved apparatuses and methods that overcomes the above-mentioned limitations and others.